Conventional heavy-duty picture frame hanger in prior art is typically a metal hanger that is anchored to wall by nail(s) positioned above a hook. A lateral projectile is provided above the hook to guide the nail into wall in an incline position. Such a nail-above-hook arrangement is not considered user-friendly because, when user is holding picture frame above hanger in an attempt to hang the metal wire of picture frame onto the hook, he needs to maneuver metal wire to bypass the lateral projectile(s) while sliding picture frame against wall in downward direction, and then engage metal wire into the hook. Such maneuvering can be time consuming and troublesome.
Conventional hook-above-nail plastic hanger in prior art may overcome the above drawback. But up to now, it does not exist a hook-above-nail plastic hanger in prior art that is capable of offering a load capacity and structural strength equivalent to that of conventional nail-above-hook metal hanger. This is mainly due to the fact that plastic material has inherent low shear/bending strength.
One motivated concept of present invention is to improve the structural design of hook-above-nail plastic hanger, and thus provide it with structural strength and load capacity equivalent to that of conventional nail-above-hook metal hanger.
Conventional nail-above-hook metal hanger in prior art also has another drawback. In order to allow the metal wire of picture frame to bypass the lateral projectile(s) and engage into the hook below lateral projectile(s), the lateral width of lateral projectile must be restricted to a minimum.
This means that nail hole in lateral projectile can't have an adequate longitudinal length to hold and support the nail within nail hole. As a result, user needs to hold both the hanger and the small nail by hand while hammering nail into wall.
Another motivated concept of present invention is to provide the lateral projectile of a hook-above-nail hanger with a sufficient lateral width, in which, the nail hole has a sufficient length to hole and support the nail, and thus enables user to hammer nail into wall while holding only the hanger without holding the small nail by hand.
It is commonly acknowledged that two (single-hook) hangers need to be installed on wall at sufficient distance apart for hanging a relatively large size picture frame in a level position. Another motivated concept of present invention is to provide a single dual-hooks hanger capable of hanging a relatively large size picture frame in level.
By conducting extensive mechanics analyses and load tests of prototypes, author of present invention is able to develop a dual-hooks and hook-above-nail hanger that offers 50 lb. (or 70 lb.) weight load capacity, provided the hanger is anchored onto drywall with two (or three) 3 d penny size nails. This weight load capacity is equivalent to that of conventional nail-above-hook metal hanger.
In U.S. Pat. No. 7,216,841, Dodig discloses a dual-hooks and hook-above-nail hanger (FIG. 6-7). But author of present invention finds that Dodig's hanger is deemed to be a light duty hanger, and can't possibly achieve the structural strength and weight load capacity of hanger of present invention. The reasons are: (1). Dodig's hanger has a substantially smaller shear stress cross-sectional area than that of hanger of present invention. (2). Based on mechanic analyses and confirmed by actual load testing, author of present invention finds that load capacity is proportional to the height of nail hole exit above the bottom end of hanger body. Dodig's hanger is deemed to be a light-duty hanger because nail hole exit is closely adjacent to the bottom end of hanger. (3). The rear leg of U hook can easily break off from base plate due to inadequate structural strength.
In U.S. Pat. No. 5,178,355, Herzig discloses a hook-above-nail hanger, in which, a leg of U hook is used for anchoring the nail. Clearly, the leg of U hook lacks of structural strength to allow Herzig's hanger to carry large load. Herzig's hanger is also deemed to be a light-duty hanger.